“Airborne molecular contaminants” or AMCs, is a term of art in the area of clean room operation, referring to gaseous contaminants. Certain gaseous contaminants cause problems due to deposition or formation of particles or haze matter on sensitive surfaces involved in a photolithography process during processing. Such surfaces include semiconductor wafers, lenses, mirrors, beam splitters, photomasks, semiconductor wafers, and pellicle films. While the detailed processes leading to particle formation is the subject of ongoing research, it is clear that they originate from gases because they cannot be eliminated by particle filtering.
A consequence of AMCs is the formation of “ultraviolet haze” on surfaces in lithography processes. Ultraviolet haze is attributed to the presence of airborne molecular contaminants which react in the presence of the ultraviolet light used in lithography to form the haze. A sensor is required to detect the presence of these contaminants and thus avoid exposing the high-value semiconductor products.
The contaminant concentration can be so low, e.g. parts per trillion, that it becomes difficult to use almost any analytical technique to investigate the contaminant composition and thus trace its origin. Existing work in the area of particle contamination produced by AMCs uses sophisticated and expensive analytical methods such as gas chromatography (GC), TOF-SIMS, and other methods to identify gaseous chemical species present regardless of whether these species cause particle deposition. These methods suffer from lack of knowledge of what contaminants will form the deposits. Attempts to discover which species are correlated with the particle formation ensue. Ultimately this could lead to understanding the chemical reactions and pathways leading to particle deposition, but it is a long and difficult process.
Another known method is to use mechanical oscillators such as piezoelectric and surface acoustic wave devices to sense the deposits by sensing their mass. This method correctly targets even unknown contaminants capable of forming the haze, but suffers from insufficient sensitivity due to mass detection limits.
Aside from detection of AMCs, removal of harmful AMCs also poses significant challenges. Gas filters and absorbers can be utilized in principle, but it is very difficult to reach the parts-per-trillion purity levels needed to prevent haze formation. A new clean room, for example, typically requires a run-in time of several weeks, during which the AMC level as indicated by haze formation gradually decreases as the sources of AMCs outgas. Therefore, elimination of AMCs that cause haze poses a significant problem. Another technique is to distill the AMCs out of the air, which is a costly process.
Methods and/or apparatuses for detection and elimination of particles formed from AMCs that are more efficient and cost effective would be welcome. Efficient and cost-effective methods and apparatuses for detection of particles formed from AMCs would also be a welcome capability.